This invention relates to machines having a reciprocating member that is coupled to a rotatable member.
In one class of such machines, particularly combustion engines, the machine includes a reciprocating piston which drives a crankshaft through a connecting rod. Such engines are subject to vibrations resulting from periodic unbalanced inertia forces of the piston, the connecting rod, and the crankshaft counterweights. Such engine designed to reduce such vibrations and cure other disadvantages is disclosed in U.S. Pat. No. 4,658,768 issued to Douglas T. Carson on Apr. 21, 1987, for ENGINE.
The machines described in this patent include a member confined to reciprocation that is coupled to the crankpin of a rotatable crankshaft by a connector which rotates in a direction opposite to that of the crankshaft with the resulting stroke being four times the crankpin offset. In these machines the reciprocating member is a piston rod connected to at least one piston and coupled through a connector to a crankpin with a resulting stroke that is four times the crankpin offset.
Machines of this nature have two unique disadvantages. One of the disadvantages is that a second degree of freedom may occur at midstroke where the motion of the reciprocating member may be zero instead of twice that of the center of the crankpin in the axis of reciprocation. This occurs when the connector rotates in the same direction as does the crank instead of the opposite direction. A second disadvantage is that as the reciprocating member nears midstroke, the connector loses its ability to transfer forces from the reciprocating member to the crankpin and vice versa. The reciprocating member and the connector may then run ahead or fall behind the crankpin resulting in high side thrust forces and possible damage.
The machine described in the aforementioned patent addresses these difficulties by using an interface between the piston rod and the crank. This arrangement has the disadvantage of being unduly complicated and increasing wear because of the engagement of the interface between two moving parts with respect to the housing.